We are using the chemostat for studying the effect of changes in growth condition on the surface components and extracellular products particularly lipoteichoic acid of cariogenic bacteria; changes being followed by chemical, serological and microscopic procedures. The organisms chosen are representative strains of streptococci, lactobacilli and actinomycetes, with studies initially concentrating on those strains whose cell wall carbohydrates-polysaccharides or teichoic acids-have been sufficiently characterized. Lipoteichoic acid is a recognized component of the membrane of most gram-positive bacteria but it may also occur extracellularly in significant amounts. These surface components are of importance in (a) identification of a particular organism and (b) in defining the nature of the organism's interaction with its environment. The bacterial cell surface is particularly sensitive to changes in growth conditions. Thus, by obtaining a clearer understanding of the effect of environmental conditions on the growth of cariogenic bacteria, we can better understand their role in inducing caries.